1. Field of the Invention
The present invention relates to a mold clamping apparatus for a die casting machine, an injection molding machine, etc., and more particularly to a mold clamping apparatus which has a space-saving apparatus construction and can easily carry out mold replacement.
2. Background Art
FIGS. 5 and 6 shows a so-called hybrid mold clamping apparatus, comprising a combination of an electrical drive mechanism and a hydraulic drive mechanism, as disclosed in, for example, Japanese Patent Laid-Open Publication No. 1998-296736. The mold clamping apparatus includes a fixed die plate 12 for mounting a fixed mold 11 thereto, and a movable die plate 14 for mounting a movable mold 13 thereto. The movable die plate 14 is disposed opposite the fixed die plate 12, and is movable right and left in FIG. 5 along a not-shown guide base provided in a base 15.
The base 15, on both sides of the movable die plate 14 (far and near sides of the movable die plate 14 in FIG. 5), is provided with a pair of drive units 16 each comprising, for example, a servo motor and a pair of mold opening/closing means each comprising, for example, a ball screw shaft 17 which can be rotated in normal and reverse directions by means of the drive section 16. The reference numeral 18 denotes a bearing rotatably supporting the front end of the ball screw shaft 17. A ball screw nut 19, mounted to the movable die plate 14, is threadably coupled to the ball screw shaft 17. The movable die plate 14 moves in a direction closer to the fixed die plate 12 by the normal rotation of the ball screw shaft 17, while the movable die plate 14 moves in a direction away from the fixed die plate 12 by the reverse rotation of the ball screw shaft 17, thus closing/opening molds.
Mold clamping cylinders 20 are provided in the four corners of the fixed die plate 12, and a mold clamping piston 21 is fit in each mold clamping cylinder 20. The right end in FIG. of a tie bar 22 is removably inserted into the mold clamping piston 21. A groove 23 is formed at the right end of the tie bar 22, and an openable/closable clamp 24, provided at the right end of the mold clamping piston 21, detachably engages the groove 23.
The tie bar 22 penetrates the movable die plate 14 and extends to the left in FIG. 5, and a large number of annular grooves 25 (which can be a screw) are formed at an even pitch in the peripheral surface of that portion of the tie bar 22 which extrudes from the movable die plate 14. Half nuts 26, which are mounted to the movable die plate 14, each detachably engage the annular grooves 26. Each half nut 26 is opened/closed by a not-shown driving device, and constitutes a coupling means for releasably coupling the tie bar 22 to the movable die plate 14.
The mold clamping apparatus performs molds opening/closing operation and molds clamping operation in the following manner, with the fixed mold 11 mounted to the fixed die plate 12 and the movable mold 13 mounted to the movable die plate 14.
When closing the molds, the half nuts 26 are opened to release the coupling between the tie bars 22 and the movable die plate 14. Thereafter, the ball screw shafts 17 are rotated to move the movable die plate 14 forward to a position shortly before the fixed mold 11 and the movable mold 13 are completely closed. Next, the half nuts 26 are closed, and the mold clamping cylinders 20 move the pistons. 21 to the right, whereby the tie bars 22 are pulled in to the right in FIG. 5 and the fixed mold 11 and the movable mold 13 are clamped firmly. When opening the molds, on the other hand, the mold clamping pistons 21 of the mold clamping cylinders 20 move to the left to push out the tie bars 22 to the left in FIG. 5 by a predetermined distance to thereby release the clamping of the molds. Thereafter, the half nuts 26 are opened to release the coupling between the tie bars 22 and the movable die plate 14, and the ball screw shafts 17 are rotated to move the movable die plate 14 backward.
The above conventional hybrid mold clamping apparatus, comprising the electrical and hydraulic drive mechanisms, is characterized by its downsized construction as compared to a mold clamping apparatus of the hydraulically-driven type that opens or closes, or clamps molds by moving a movable die plate 14 by means of a cylinder or a link mechanism directly coupled to the movable die plate 14.
The conventional hybrid mold clamping apparatus, however, has the following problem involved in mold replacement operation: FIG. 6 shows the position of the movable die plate 14 upon mold replacement. As shown in FIG. 6, in order to perform a mold replacement operation, it is necessary to pull the right ends of the tie bars 22 out of the fixed die plate 12 so as to secure a space for mold replacement on the mold-mounting side of the fixed die plate 12.
Thus, in order to smoothly perform mold replacement with the conventional mold clamping apparatus, the apparatus must be designed to be capable of moving the movable die plate 14 further backward from the maximum backward limit position in usual opening/closing of molds to the position shown in FIG. 6. The conventional apparatus, therefore, employs such a long moving stroke of the movable mold 14 as to enable the tie bars 22 sufficiently move away from the fixed die plate 12, thereby securing an operating space for smoothly performing mold replacement. It is, therefore, necessary to use a long base 15, ball screw shafts 17 with a long stroke, etc. solely for mold replacement, which poses an obstacle to further downsizing of the apparatus.